The present invention relates to hot manifold assemblies for plastic injection molding machines and for the injection stage of plastic injection blow molding machines. More particularly, the present invention relates to a hot manifold assembly having inherent flexibility over a wide temperature range permitting the fixed positioning of the manifold with respect to both an associated plasticating injection unit and a multi-inlet or multi-cavity mold assembly.
Conventional multiple cavity molds are widely used in injection molding machines to simultaneously produce a plurality of similar articles. To supply these multiple cavity molds, heated plastic must be equally distributed to each mold assembly, with precise plastic volumes, packing pressures, and temperature ranges being maintained over many molding and release cycles. It is conventional to achieve the precise volumes and pressures by adopting constant path length designs for the manifold assembly, typically using an X or H manifold design format. It is also desirable to minimize sharp corners in the manifold to reduce the shearing action on the plastic as it travels through the manifold. Since this heated plastic would ordinarily cool to an unacceptably low temperature during transport through such a manifold to each separate mold assembly, it has been known to artificially heat the manifolds to help maintain the plastic within a defined temperature range to maintain the desired fluid and other characteristics.
However, heating typical X and H design format manifolds can cause alignment problems between the hot manifold outlets and the inlets of the mold assembly. When the manifold is heated, it expands, the amount of expansion generally being a function of the net path length between the manifold inlet and each of the outlets. This expansion varies the alignment or positioning of each manifold outlet in relation to the adjacent mold assembly inlet, and can cause difficulties in sealing the manifold to the mold assembly and in operation of the gate valves controlling the introduction of the plastic into the mold assembly inlets.
Various solutions to this problem have been proposed. For example, Bright, et al., U.S. Pat. No. 4,219,323, discloses a block-like for coupling various portions of a hot manifold together, the link including slots allowing for expansion and contraction compensation. Roy, U.S. Pat. No. 4,333,629, discloses a floating manifold which is telescopically coupled to the supply tube and to delivery tubes associated with each cavity to permit relative movement under varying temperature conditions. Schad, U.S. Pat. No. 4,588,367, discloses a conventional manifold coupled to a multi-cavity mold by thermal expansion support elements at the joint between the manifold and the nozzle which include undercuts which provide the required flexibility. Benenati, U.S. Pat. No. 5,032,078, discloses a manifold sealed with metals having a dissimilar coefficient of expansion to improve sealing efficacy, and supporting removable tips that can be fitted to adjust the overall length of heated bushings that are included in the manifold. Gauler, U.S. Pat. No. 5,269,677, discloses a hot manifold system having sprue bushings including annular grooves adjacent the connection with a conventional block manifold which create points of flexure to accommodate dimensional changes due to temperature changes during use. However, none of these structures has proven to be entirely satisfactory in all melding situations requiring compensation for thermal expansion.
What is needed is a manifold assembly that inexpensively provides plastic maintained within a predetermined temperature range to multiple mold assemblies. The manifold assembly must have outlets which are fixed in position with respect to the mold assemblies yet must allow for thermally induced stresses to be released. Further, the distributing manifold should allow an arbitrary number of mold assemblies to be accommodated thereby according the designer full flexibility in utilizing machines of various size and capacity.